The present invention relates to a method for patterning a chemically amplified positive resist material which provides novel solubility characteristics suitable for microfabrication.
Deep-ultraviolet lithography, one of a number of efforts currently being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, is thought to hold particular promise as the next generation in microfabrication technology. Deep-UV lithography is capable of pattern generation to dimensions of 0.25 .mu.m or less and, when a resist material having low light absorption is used, can form patterns with sidewalls that are nearly vertical to the substrate. One technology that has attracted a good deal of attention recently utilizes a high-intensity KrF excimer laser as the deep-UV light source. Resist materials with low light absorption and high sensitivity are needed to successfully apply this technology to large-volume production.
In light of this, recently developed acid-catalyzed chemically amplified positive resist materials (e.g., JP-B 27660/1990 and JP-A 27829/1988), with their high sensitivity, high resolution and good dry-etching resistance, have excellent properties which make them especially promising as resist materials for deep-UV lithography.
The strong influence of solubility characteristics on the resolution of resist materials has been a subject of debate since the days of novolak-based resist materials. In particular, it is generally well-known that the resolution becomes higher as the tan .theta. (.gamma. value) increases, and it has been reported (T. Ohfuji, K. Yamanaka and M. Sakamoto: Proceedings of SPIE, 920, 190 (1988); T. Kokubo: Tech. Proceedings of SEMI Technol. Symposium, 86 (1991)) that approaches such as optimizing the structure of novolak resin in order to increase interactions with the resin (M. Hanabata, A. Furuta et al.: Proceedings of SPIE, 771, 85 (1987)), designing sensitizers having a large dissolution-inhibiting effect (C. R. Szmanda, A. Zampini, D. C. Madoux et al.: ibid., 1086, 363 (1989)), and providing novolak resins with a "stonewall" structure (M. Hanabata, Y. Uetani et al.: ibid., 920, 349 (1988)) have the effect of altering the dissolution rate with respect to exposure from a monotonically increasing relationship to a sigmoid relationship, enhancing tan .theta. and improving the resolution.
However, we found through investigations that, particularly in the case of chemically amplified positive resist materials, merely increasing the slope of dissolution rate versus exposure does not by itself necessarily lead to increases in the resolution and focal depth, and so we set out to resolve this problem.